Abstract

Ventilation of underground mines is required to dilute and remove hazardous gases, control heat and provide oxygen for workers and machinery. Kahatagaha- Kolongaha mines, Dodamgaslanda was selected for the present study as it was restarted recently and therefore very little research has been done on air quantity and quality of the mine. The objectives of this research are to make a proposal to rectify the existing ventilation system and to upgrade the existing airflow system with modifications to the present system. A detailed ventilation survey was carried out by measuring the variations of airflow, pressure drop and humidity differences along four levels of the mine (i.e. 565ft, 805ft, and 965ft and 1132ft levels) and compared with the corresponding standard values which describe the lowest conditions to be met for working underground. The distributions of airflows, pressures and humidity in each level could be detailed on graphs and the areas where the additional air supplies were identified. It was proposed to install a dehumidifier to reduce the humidity level inside the mine. Suggestions were made to improve the present ventilation system by locating two booster fans in level 565 ft and 805 ft, which will enhance mine air quality increasing health and safety aspects of underground environment.

Keywords: Air quality, Ventilation survey, Humidity, Dehumidifier

Acknowledgement

We are thankful to Prof. U.G.A. Puswewala and the staff of Department of Earth Resources Engineering of University of Moratuwa for facilitating this work.

Our sincere gratitude goes to Mr. D. Kalansooriya the Chairman and also to Mr. R. Manchanayake, Senior Technical Officer and the staff of Kahatagaha Graphite Lanka Limited for helping with the field work and providing guidance in every aspect.

Contents

1.0 Introduction......................................................................................................................1

1.1 Subsurface Ventilation........................................................................................................................1

1.2 Objectives of subsurface ventilation...................................................................................................1

1.3 Objectives...........................................................................................................................................2

2.0 Literature Review.............................................................................................................3

2.1 Subsurface Ventilation Systems..........................................................................................................3

2.2 Mine systems.......................................................................................................................................3

2.2.1 Fans....................................................................................................................................4

2.2.2 Stopping and seals.............................................................................................................4

2.2.3 Doors and airlocks.............................................................................................................4

2.2.4 Regulators .........................................................................................................................5

2.2.5 Air crossing........................................................................................................................5

2.2.6 Location of mine fans........................................................................................................5

2.2.7 Gas control……………………………………………………………………………….6

2.2.8 Transportation……………………………………………………………………………7

2.2.9 Fan maintenance…………………………………………………………………………7

2.2.10 Fan performance………………………………………………………………………..7

2.2.11 District system………………………………………………………………………….8

2.2.12 Auxiliary systems………………………………………………………………………9

2.3 Ventilation Surveys............................................................................................................................9

2.3.1 Air Quantity Surveys........................................................................................................11

2.3.2 Instruments for airflow measurements.............................................................................11

2.3.2.1 Rotating vane Anemometer............................................................................11

2.3.2.2 Swinging vane anemometer (Velometer).......................................................12

2.3.2.3 Vortex-shedding anemometer.........................................................................12

2.3.2.4 Smoke tubes....................................................................................................12

2.3.2.5 Hot body anemometers...................................................................................12

2.3.3 Traverse Methods for airflow measurements...................................................................12

2.3.3.1 Moving Traverse.............................................................................................12

2.3.3.2 Fixed Point Traverses......................................................................................13

2.3.3.3 Method of equal area………………………………………………………..14

2.3.3.4 Log-Linear Traverse…………………………………………………………14

2.3.3.5 Velocity Contours............................................................................................14

2.3.4 Measurement of cross-sectional area……………………………………………………15

2.3.5 Pressure Surveys…………………………………………………………………………16

2.3.5.1 Gauge and Tube Surveys……………………………………………………..16

2.3.5.2 Barometer and Altimeter Surveys..................................................................17

2.3.2 Air Quality Surveys…………………………………………………………………….17

2.3.2.1 Measurement of water vapour in air (Humidity)...................................17

2.4 Mine Atmosphere..............................................................................................................................18

2.4.1 Mine Gases.......................................................................................................................18

2.4.1.1 Mine Air & its Components............................................................................19

2.4.1.2 Noxious Gases (Explosive).............................................................................20

2.4.1.3 Noxious Gases (Non Explosive).....................................................................21

2.4.1.4 Toxic Gases (Explosive).................................................................................22

2.4.1.5 Toxic Gases (Non-Explosive).........................................................................24

2.4.2 Smoke...............................................................................................................................26

2.4.3 Mine Damps......................................................................................................................26

2.4.4 Mine Dust..........................................................................................................................27

2.4.4.1 Classification of the dust..................................................................................27

2.4.4.1.1 Size of aerosol particles..................................................................27

2.4.4.1.2 Physiological effects of dust...........................................................28

2.4.4.2 Reasons for dust……………………………………………………………...29

2.4.4.3 Influencing parameters of dust control………………………………………30

2.4.4.4 Control of dust in mines………………………………………………………31

2.4.4.4.1 Methods of dust control…………………………………………..31

2.4.4.4.2Methods of dust control in underground mine environment…….32

2.4.4.5 Problems due to dust……………………………………………….33

2.4.4.6 Standards……………………………………………………………34

2.5 Mine Fans...........................................................................................................................................34

2.5.1 Axial and Propeller Fans....................................................................................................36

2.5.2 Centrifugal fans (Radial fans)............................................................................................36

2.5.3 Fan pressures....................................................................................................................38

2.5.4 Impeller theory and fan characteristic curves.....................................................................40

2.5.4.1 Theoretical characteristic curves for a centrifugal impeller..............................41

2.5.4.2 Characteristic curves for an axial fan................................................................42

2.5.5 Fan laws..............................................................................................................................43

2.5.6 Fans in combination............................................................................................................43

2.5.6.1 Fans in series.....................................................................................................44

2.5.6.2 Fans in parallel..................................................................................................45

2.5.7 Fan Performance.................................................................................................................45

3.0 Methodology....................................................................................................................47

3.1 Selection of survey stations...............................................................................................................47

3.2 Air quantity survey............................................................................................................................47

3.3 Recording of humidity values...........................................................................................................48

3.4 Pressure survey..................................................................................................................................48

4.0 Results and Discussion....................................................................................................49

4.1 Cross sectional area...........................................................................................................................49

4.2 Air Quantity.......................................................................................................................................50

4.3 Humidity............................................................................................................................................52

4.4 Air Pressure.......................................................................................................................................54

4.5 Discussion..........................................................................................................................................55

5.0 Conclusion and Recommendations.................................................................................57

References...............................................................................................................................58

Appendices..............................................................................................................................59